This invention relates generally, as indicated, to apparatus and method for making forming tubes out of paper or the like, including particularly the apparatus and method by which one or more beads are formed on the outer periphery of the tubes during manufacture.
During the processing of glass fiber, molten glass is passed through one or more drawing dies which produce a number of very fine glass fiber filaments that are formed into a single strand and subsequently wound around the outer surface of paper forming tubes. After the desired amount of glass fiber has been wound on the forming tubes, the glass fiber is further processed, following which the forming tubes are partially collapsed and removed from the interior of the glass fiber windings so that the glass fiber can be unwound by grasping the interior end. Because of the method of processing glass fiber, such forming tubes must have good wet strength and be resistant to both heat and centrifugal forces. Also, the forming tubes must be sufficiently flexible to permit them to be partially collapsed so that they can be removed from the interior of the glass fiber windings.
It is conventional practice to make such forming tubes by helically winding a plurality of separate plies of paper or paper-like material around a stationary mandrel and bonding such plies together using a suitable water-resistant adhesive as disclosed, for example, in U.S. Pat. No. 4,026,690, the disclosure of which is incorporated herein by reference.
Also, it is conventional practice to provide such forming tubes with one or more beads or ridges on the exterior surface of the forming tubes, formed by depositing one or more cords between selected tube plies during the tube manufacture. Such beads help to retain the glass fibers on the forming tubes during the winding process. To prevent the glass fibers from tracking along the beads as they are wound around such tubes, one of the beads may be laid down in an irregular weave pattern. For ease of manufacture, the beads were generally made to extend all the way to the end edges of the forming tubes. However, as is well known, that can result in the bead ends working their way out of the tube end edges even though the forming tubes are sealed along the tube edges. When this occurs, the ply laminations will pull apart and allow water to get in between the plies where the beads exit from the forming tube edges, thus causing premature delamination, which severely limits the number of times the forming tubes can be used.
It has long been known that this type of delamination can be substantially eliminated by terminating the beads inwardly (i.e., short of) the end edges of the forming tubes. However, heretofore there was no known apparatus and method for producing such forming tubes on a commercial scale of the desired high quality and uniformity.